The olive is a fleshy fruit which, in its natural state, is imbued with an extremely bitter taste which is produced by tannin and other organic acids present in the fruit. Without neutralization of these acids, olives are essentially inedible and are useful only in the production of olive oil. However, with appropriate processing olives are considered by many to be a desirable condiment.
Generally, olives may be processed into two distinct forms known as Spanish green olives and ripe (dark) olives. The processes for the production of each of these two kinds of olives both employ alkaline solutions to at least partially neutralize the acid flesh of the olive. For example, in preparing Spanish green olives the appropriate olives are totally immersed in a lye solution until the lye penetrates about 1/8 inch into the flesh, and then the olives are transferred into a brine-holding solution for partial fermentation. This results in an olive having a flesh pH of about 3.5 and an increased salt content which produces the slightly bitter taste associated with Spanish green olives. During these process steps, any exposure to air is avoided so that oxidation, which produces a darker color, does not occur.
However, with respect to ripe olives, often described as black ripe olives, the effect of oxidation is employed to advantage. In a ripe olive process, the olives are soaked in a dilute lye solution not only to neutralize the acids in the olive to give the preferred taste, but the olives are exposed to air so that the flesh is oxidized to a darker color. For ripe olives, the dilute lye solution is administered in several repetitive steps to develop a dark oxidation ring at the surface of the olive, ending with a "pit lye" step wherein the alkaline solution is allowed to penetrate through the olive flesh to the pit of the olive. The total penetration of the olive flesh by the lye solution results in a nearly neutral pH, e.g., between 7.0 and 8.0.
An older dry process, now largely abandoned, for the production of black ripe olives comprises the treatment of the olives in a dilute lye solution for about three hours followed by the exposure of the olives to air with intermittent fresh water rinsing for one to two days. The lye and exposure steps are repeated until the color change is complete. The total processing time for complete coloration in this process is approximately three weeks, and the intermittent rinsing is required to avoid shriveling and contact marking of the olives thought to result from the constant exposure to lye and air.
A wet process, developed in the late 1940's, has provided significant advantages over the more traditional dry process. The wet process involves alternating the lye solution step with an air-sparged (agitated) fresh water rinse. This has replaced the alternating air-exposure and rinse steps and oxidizes the flesh of the olives by bubbling air through the alkaline solution.
More specifically, during a five- to seven-day period unprocessed olives are immersed in a 0.5 to about 1.5% solution of sodium hydroxide (a lye solution) for periods of from two to twenty-four hours over four to seven days. The strength of the alkaline solution may also be adjusted lower for fresh olives (0.5 to about 0.7%) and higher for storage olives (0.9 to 1.5%), that is, olives which have been stored in a brine solution. As used herein, the term unprocessed olives refers to olives which have yet to undergo complete neutralization of the olive flesh, and includes both fresh and storage olives.
Between each lye immersion, the sodium hydroxide is rinsed from the olives by a succession of from two to eight fresh water rinses. Often, mineral acids such as sulfuric and hydrochloric are added to the rinse water to a pH of 3.0 to 4.5 to assist in removing and neutralizing the lye solution from the surface and flesh of the olive. Typically, in the first lye application the flesh of the olive will be permeated by the sodium hydroxide solution to a depth of from 1/32 to 1/16 of an inch. Upon oxidation by sparged oxygen (air) the neutralized portion will begin to oxidize and darken in color. Each further lye application will progressively increase both the shade of the color and the penetration of the color into the meat of the olives. Generally, between 1/16- and 3/16-inch penetration of an oxidation ring is set into the olives over the course of about a three-day period. Once this color has been set in the oxidation ring to the desired level of penetration, a sustained twenty-four hour lye immersion is applied to the olives until the lye solution reaches the pit of the olive. This step is thus known in the industry as the "pit-lye" step, and results in the flesh of the entire olive being raised to a pH of about 13-14 to neutralize the so-called "bitter principal" of the olives. Without this pit-lye application, the un-neutralized flesh of the olives remains so bitter as to be inedible.
Following this pit-lye application, the alkaline residue is rinsed from the olives by repeated fresh water rinses over the course of approximately a twenty-four hour period, with the water being changed about every four hours, until the pH of the olive flesh is reduced to pH 9-10. Mineral acids are not employed to neutralize the alkaline flesh, as the olive has been found to bleach from the low pH required to neutralize the substantial amount of lye in the olive flesh. It will be appreciated that this method of neutralization results in the use of substantial amounts of fresh water. It is also known to employ carbon dioxide as a sparging medium in this final rinse step both to place carbon dioxide in solution with the rinse water and to assist in stirring the olives.
The remainder of the olive treatment process heretofore known consists of treating the olives in a heated water bath of approximately 140.degree.-160.degree. F. for approximately twenty-four hours. This increased temperature is thought to open the pores in the olive skin and assist in withdrawing the lye from the olive at a faster rate. Without heat, lye neutralization has required about two weeks, although this time period may be reduced to four to five days if mineral acid is used to assist in this process. Moreover, this extensive application of heat has traditionally been the only way to develop the preferred dark brown-black olive desired in a black ripe olive within a commercially-acceptable period of time. Without heat, the olives develop a dark brown color at best. Even though the cost of heating the rinse solution is substantial, this step has been considered indispensable in producing high-quality black ripe olives. This heating step is sometimes referred to as a pasteurization process, even though it is not directly related to the inhibition of fermentation.
Following the pasteurization step, there follows approximately a twenty-four hour period during which the olives are cooled along with the heated pasteurizing water. Subsequently, the olives are canned and sterilized according to known methods.
Various iron salts have also been employed for some time in the fixation of color in ripe olives. For example, between five and twenty parts per million of iron in the form of ferrous sulfate, ferrous ammonium sulfate, ferric chloride or ferrous gluconate will fix, i.e., set, the color of black ripe olives. It has been stated that the olives must first be processed to get a good color or the iron salts will not fix the color. In other words, the iron salts will not compensate for poor processing or for poor olives. With respect to the particular iron salts which are used, the most commonly employed salt is ferrous gluconate, primarily because it is the only iron salt approved by the U.S. Food and Drug Administration for use in food products. However, other iron salts have been shown to have an equal or better effect.
In the prior art processes, the ferrous gluconate is added during the pasteurization process, when the pH of the olive flesh is from pH 9 to 10. Since it is well known that heat greatly hastens color fixation, the gluconate is applied at the pasteurization temperatures.
It should be apparent from the description that the processing of black ripe olives has traditionally consumed substantial amounts of energy and water. First, the processing tanks are of considerable size and often retain in excess of 2,500 gallons of solution and many tons of olives. To neutralize the olives after the pit-lye step by changing this amount of water every four hours for a twenty-four hour period produces substantial amounts of waste water which must either be properly disposed of or reprocessed to remove alkaline material. Second, to heat this amount of solution to pasteurization temperatures requires a considerable amount of energy, and thereafter cooling the olives to canning temperature consumes further cooling water, expense and time. In addition, the overall processing time for a batch of olives is critical in that olives should preferably be processed quickly after harvest, and any extensive time period for processing increases storage costs and fruit spoilage.
While demand and economics require faster and more efficient processing, the consumer continues to demand an olive which has a black flesh and an even darker black skin and oxidation ring, and a uniform color from the ring to the pit of the olive. Since the lye progresses through different olives at different rates, some olives will cut (be penetrated by the lye solution) much faster than others. Since the olives cannot be processed individually, attempts to accelerate the curing process have always resulted in a substantial increase of the number of off-color olives which must eventually be separated, manually, prior to canning. In today's market, the consumer demands black ripe olives which are consistently and uniformly black, and will not tolerate variations in color. Even with stringent controls and state of the art processing techniques, such as those described in U.S. Pat. No. 4,463,023 (the teachings of which are hereby incorporated by reference), it is not uncommon to have returns from consumers which are due solely to the color of the olives.
Accordingly, it has been a desideratum to increase both the efficiency of the ripe olive treating process, and to provide a more uniform color in such fruit.